To better understand the advantages and improvements achieved with the present invention, a brief discussion of tire construction and building procedures follows. A pneumatic tire is typically constructed by applying various components, or plies of the tire as flat stock, upon a rotating tire building drum to form a hollow, toroidal shaped green or uncured tire. The order of applying the components is as follows: first, an innerliner is wrapped upon the tire building drum; the innerliner is followed by carcass plies containing tire reinforcement, the carcass plies are followed (not necessarily in the following order) by the beads, apexes, chaffers, side walls, belts and tread. The components are then expanded and formed into a toroidal shaped, green tire assembly, in a manner well known in the art. The green tire assembly is then removed from the tire building drum and placed into a shaping and vulcanizing mold having the shape of the finished tire.
In the conventional manner, the mold is sealed and the toroidal shaped green tire assembly is heated and expanded radially outward into the mold periphery by injecting pressurized gas or fluid into a curing bladder mounted within the mold and disposed within the green tire assembly. As the curing bladder expands, it forces the tread and sidewalls of the green tire assembly into contact with the heated mold walls to shape and vulcanize the green tire assembly into a fully vulcanized tire. During the radial expansion of the green tire assembly within the shaping and vulcanizing mold, the toroidally shaped plies expand radially outward to dimensions beyond those of the original green tire assembly. Therefore, the bladder is usually made of an expandable elastomeric material, such as butyl rubber, which also provides resistance to the steam or hot water used to force the tire against the mold surface.
During the production of tires on an assembly line, the curing bladder within the shaping and vulcanizing mold periodically wears out or fails. The tire industry has tried to eliminate the need for a curing bladder used in tire production. U.S. Pat. No. 4,166,883 discloses a method of forming a cured tire in a mold without a bladder. Instead of a bladder, the liner functions as the impervious layer. The liner is cured or partially cured to produce a steam- and water-resistant surface before the remainder of the tire is cured in a mold. The curing or partial curing is accomplished by electron irradiation.
In an effort to eliminate several steps involved in the tire building process, U.S. Pat. No. 5,762,740 discloses a method and apparatus for simultaneously forming, positioning, attaching and conveying a plurality of continuous strips of elastomeric tire components to adjacent strips of tire components as they are conveyed. This “contoured calendaring” process produces a laminate suitable for use as a subassembly for a pneumatic tire. The apparatus employs a plurality of calender rollers and each tire component has a predetermined cross sectional profile formed by a component-forming depression on an associated calender roller. Each component of the subassembly is in an uncured state prior to the subassembly being placed in the shaping and vulcanizing mold.
The present invention is directed to a method for providing a pre-cured innerliner for use in a pneumatic tire subassembly in order to provide the advantages of use of a bladder-less shaping and vulcanizing mold. Although the methods described herein are applicable to any size of finished pneumatic tire, the invention is specifically directed to methods for forming off-road and farm tires having large nominal rim diameters. It is appreciated by those skilled in the art that practices useful for passenger and light truck pneumatic tires are not always practical to apply to large off-the-road earthmover or farm vehicle tires.